HELENA, Mont. - A group of U.S. senators, including Maine's Olympia Snowe, called a May 11 deadline for compliance with federal Real ID rules "arbitrary and ineffective," and asked the Department of Homeland Security to exempt states from it.

Maine and New Hampshire are among the few states that have so far have refused to seek an extension to identification rules by March 31, which Homeland Security says would be good enough at this point to comply with the May 11 deadline.

The agency says residents from noncompliant states could face extra screenings at airports and federal buildings.

New Hampshire Sen. John Sununu, a Republican, joined Snowe and Democrats Max Baucus and Jon Tester of Montana, and Daniel Akaka of Hawaii, in sending a letter Wednesday to Homeland Security Secretary Michael Chertoff. It asked him to scrap the deadline or answer their questions about the process.

Homeland Security has said a driver's license will not qualify as legal identification at airports and federal buildings after May 11. Montana, Maine, South Carolina and New Hampshire are the only states that have not complied with the deadline.

The senators said Homeland Security acknowledges that none of the states will actually comply with legislative identification requirements. And full implementation of Real ID is on hold until 2017.

If the agency does not lift the deadline, the senators said Chertoff needs to tell them why state residents could face secondary screening and what that additional screenings would entail, if anyone would be prevented from boarding airplanes, and other questions.

The Maine, New Hampshire and Montana legislatures passed laws that prohibit those states from complying with the Real ID act.